DE4129610A1 - LEVEL CONTROL SYSTEM FOR MOTOR VEHICLES - Google Patents

Description

The invention relates to a level control system for Motor vehicles, which essentially consist of vibration dampers, between the individual wheels and the vehicle body are arranged from electrically operated valves with de NEN a pressure medium flow between a (central) pressure source, an unpressurized memory, the vibration dampers and Druckbe assigned to the individual vibration dampers is controllable from displacement sensors to determine the Body height and body movements, from sensors for direct or indirect determination of the vehicle speed and the steering angle and from an electrical circuit arrangement voltage that evaluates the sensor signals and the one rule circuit contains which depending on a setpoint and the actual value of the body height of the vehicle under consideration consideration of a permissible deviation between target and Actual value generates the valve actuation signals.

Level control systems of this type are known. They serve for Compensation for unwanted level changes due to Be load changes, lane excitations and certain driving maneuvers. While transient conditions, e.g. B. Vibrationsvor gears can be remedied by a damping force control Movements in stationary longitudinal and / or transverse movements  accelerations are not changed by vibration damping or to be influenced. To overcome such stationary Zu stands, such as bank angles when cornering and braking and Starting off, is the "classic" active chassis control known in connection with a hydraulic cylinder Energy source the conventional spring / damper elements set and the over a position control loop The vehicle is leveled and the level is adjusted. The systems of this type previously implemented use expensive, fast switching servo valves and have a high Energy requirements. Since only reactions, namely movements of the Vehicle, and not actions such as steering maneuvers, who senses dead time problems occur in some cases.

From European Patent No. 2 19 864 is already known a level control system with which by steering caused rolling motion of the vehicle can be suppressed should. For this, the associated calculation and tax is calculated device based on vehicle speed and steering wheel a so-called prediction roll angle for the vehicle construction. If the absolute value of the prediction roll angle becomes greater than a predetermined threshold, tax signals for reducing the roll angle are output. It han is a control, not a regulation, because no feedback of the actual roll angle correspond signal. The forecast roll angle is small The vehicle level is dependent on the threshold value speed of the difference between the actual and the setpoint of the Vehicle height kept in a predetermined range; Rule size is not the prediction roll angle in this case,  but the height difference.

The invention is based on the object, a level control system to create situations that affect the vehicle influence level, quickly recognize and appropriately reacted to these influences. The system is said to have high control quality unite with low power requirements, and it should with relatively low manufacturing costs can be realized.

It has been found that this task is accomplished by a Level control system of the type mentioned is to be solved, whose peculiarity is that this one the Change in longitudinal and lateral acceleration, d. H. the jerk of the vehicle body evaluating circuit whose Output signal of the control circuit can be fed and the target worth the build height shifts when the jerk hits a threshold value exceeds, the direction of displacement of the Direction of change is dependent, and that the longitudinal and Lateral acceleration of the vehicle body evaluating shift circuit is present, the output signal of which the permissible Ab deviation of the actual value from the setpoint of the body height or the permissible system deviation varies.

According to the invention, the observation of the jerk recognized before the appearance of the body movement that a Situation exists in which larger building movements were to be expected ten, and by a consequent shifting of the Target levels reached an earlier start of the control. In addition, depending on the longitudinal and transverse be acceleration of the vehicle the permissible  Actual value / setpoint deviation defined by, depending on Situation, on the one hand, reaching the target particularly quickly value and on the other hand an overcompensation of the To prevent roll.

According to an advantageous embodiment of the invention the setpoint of the body height is adjusted individually by one wheel given amount raised or lowered as soon as the jerk a predetermined positive or negative threshold steps. It can be used to change the setpoint overall height also several threshold values depending on ent speaking threshold values of the jerk.

Another embodiment of the invention consists in that one by the circuit that evaluates the jerk caused shifting of the body height setpoint permissible control deviation from the target value or the so-called Re difference remains. The permissible control deviation is, however, around a predetermined threshold, in several Stages or continuously depending on ent speak speaking values of the longitudinal and lateral acceleration increased or increased. A significant improvement in comparison Known systems are already change of the permissible control deviation depending on reached a single threshold.

According to the invention, the longitudinal accelerations are expediently and the change in the longitudinal acceleration of the vehicle construction with the help of wheel or axle speed sensors the measured values calculated or derived from these measured values  headed. The change in the longitudinal acceleration of the vehicle construction is based on the brake pressure curve, the brake pedal travel, from the throttle valve angle of the vehicle drive motor approximately derived from the pitch angle etc. The Querbe acceleration and the change in the lateral acceleration of the Vehicle body is according to an embodiment of the Er the steering angle speed and the vehicle ge speed and / or determined from the roll angle.

So that the regulation can start early, after a another embodiment of the invention, the pressure source activated, e.g. B. by switching on a pressure medium pump, so as soon as the jerk exceeds a predetermined threshold. This is the case for systems without a central pressure accumulator from special meaning.

The level control system according to the invention is expedient designed as a four-channel control system, with each wheel a displacement sensor is arranged and the body height on each wheel is individually adjustable.

In a particularly inexpensive embodiment, the System a central pressure supply system with a electric motor driven hydraulic pump, with a central pressure accumulator and with hydraulic valves in the Connections to the hydraulic pump and the pressure accumulator as well are inserted in the way to the surge tank where in the pressure supply system over one each in the rest blocked hydraulic valve that can be switched to flow to the individual vibration dampers with the associated ones  Pressure vessels is connected. Such a system is needed So only simple 2/2-way valves.

According to another embodiment of the invention the four-channel level control system is a central pressure supply with a hydraulic pump and with a pressure relief equal tank, the pressure supply via one in each Locked hydraulic valve at the vibration position damper is connected. In a second switch position of the hydraulic valve is the vibration damper with the Expansion tank and in a third switching position the hydraulic pump is connected to the vibration damper. In this embodiment are in one from the print side of the hydraulic pump to the surge tank Pressure medium path and immediately before connecting the pressure off equal container one in the rest position on passage switched isolating valve inserted. In addition, the Pressure side of the hydraulic pump and before the isolating valve, that too leads to the surge tank, one pressure sensor each arranges.

Finally, according to another embodiment, the Erfin the level control system with a monitoring circuit equipped, which determined with the help of the displacement sensors Body heights and body movements, the pressure curve or Pressure changes in the level control system, e.g. B. in the individual Pressure vessels or in a central pressure accumulator tet and if the measured values or ver equals occur, triggers an error signal that by Activate the hydraulic valves or block the on  control switches the system into a safety state.

Other features, advantages and possible uses of the Invention go further from the following description Details can be seen from the attached illustrations.

It shows

Fig. 1 schematically shows the main functional blocks and the signal of a control system according to the invention,

Fig. 2 is a graph illustrating the setpoint adjustment and the control difference variation,

Fig. 3 in block diagram the main components of a control system according to the invention and the signal path,

Fig. 4 schematically and simplified the main hy draulic components of a control system according to the invention and their interconnection and

Fig. 5 in the same representation as Fig. 4 shows another embodiment for the hydraulic design of a control system according to the invention.

Illustrates the representation of the functional blocks of FIG. 1 light the basic structure of a control system according to the invention. In a function block 1 , the elements or circuits for regulating the installation height, that is, the controller itself are summarized. The components shown symbolically form a so-called structure-variable controller. The won with the help of (not shown) damper displacement sensors path information s _a , symbolized by the block 4 , namely namely via a proportional transformer 5 or via a low-pass filter 6 to a threshold circuit 7 . The output signal of the circuit 7 controls valves and thus causes - represented by the function blocks 8 , 9 and 10 - maintaining the current prevailing in the vibration damper pressure 8 , increasing the pressure 9 or a pressure reduction 10th The output signal of the threshold circuit 7 is also fed back via a signal path 11 , because in the controller 1 the input of the circuit 7 depending on the output signal of this threshold circuit 7 according to a predetermined algorithm either to the output of the proportional transformer 5 or to be turned on at the output of the low pass 6 . In the older German patent application DE 40 09 234 A1 such a structurally variable controller is described ben. In principle, however, other controllers can also be used for the task of function block 1 in FIG. 1.

The target level s _d is given to the controller in function block 1 by the output signal of a circuit 12 .

With the aid of the threshold value circuit 7 , the pressure control valves, which perform the functions of the blocks 8 , 9 and 10 , are consequently controlled as a function of the difference between the desired and the actual level (Diff = s _a -s _d ). The permissible control deviation is predetermined by the threshold values of the circuit 7 , which only allow a reaction to the input signal of this circuit, the control difference Diff, when a positive or negative threshold value delta is exceeded. The valves are operated in the following way:

• - If the difference is smaller than the threshold delta, the valves are switched to pressure maintenance ( 8 ).
• - If the difference is greater than + delta, pressure is reduced ( 10 ).
• - If the difference is less than -delta, the pressure is increased ( 9 ).

The changes in the longitudinal and lateral acceleration a _l and a _q , namely the jerk, are recorded and evaluated in a function block 2 . A circuit 13 is used to determine the jerk, which is derived from the information obtained with the help of wheel or axle speeds, from the Bremsdruckver, the brake pedal travel, the throttle valve angle of the drive motor, from the pitch angle or from a combination of some of these variables or approximately can be calculated.

A threshold circuit 14 , which is connected to the output of the circuit 13 used to determine the jerk, determines whether the jerk is within predetermined limit values or whether it exceeds the threshold values + _o , - _o . As soon as the jerk exceeds or falls below the predetermined positive or negative threshold value, the output signal of the circuit 14 raises or lowers the desired level s _d via a signal line 15 , as will be explained in more detail with reference to FIG. 2, depending on the direction of the jerk.

The evaluation of the jerk determines whether there is a situation for which larger body movements are to be expected. If the jerk exceeds the predetermined threshold le, the target level s _{d is} shifted by a certain amount.

In the illustrated embodiment, the jerk is compared only with a single positive and a negative threshold value, but it is also entirely possible to provide several threshold values or to continuously shift the target level as a function of the jerk. The permissible value ± d _{o of} the control difference Diff or the permissible deviation of the actual value s _{a of} the body height from the target value s _d is not changed when the target level is shifted by the output signal of the function block 2 .

However, this tolerance range or the permissible control deviation ± d _o is also variable according to the invention, depending on the longitudinal and lateral acceleration a ₁ , a _q . In function block 3 , namely the acceleration a, which is determined with the aid of a circuit 16 , is evaluated via a further threshold circuit 17 . As long as the longitudinal and lateral acceleration a _l , a _{q are} low, a relatively large control deviation Diff from the target value s _{d is} permitted. However, if the longitudinal and lateral acceleration exceed a predetermined limit value ± a _o , which the threshold circuit 17 defines, the permissible control deviation from the target value s _{d is} reduced via a signal line 18 in order to increase the control speed of the level control system.

The interaction of the various threshold values explained with reference to FIG. 1 is now explained with the aid of the graphical representation in FIG. 2. The four columns show different situations AD. In the first situation A, both the jerk and the acceleration are smaller than the relevant thresholds. In this situation, the basic setting comes into effect, in which the damper travel or the actual value s _a can fluctuate within the limits +1 without the controller causing a change in pressure. Exceeds the actual value of s _a value of "1", causing the controller a pressure reduction, whereas when the actual value falls below _a = s "-1", the pressure is increased.

Situation A describes the initial situation. The pressure maintenance range is symmetrical to the setpoint or setpoint s _d . There is a relatively large permissible control deviation, which leads to a minimization of the control activity due to disturbance variables.

If the jerk in situation B now exceeds the predetermined threshold value a ₀ , which is recognized by the threshold value circuit 14 in FIG. 1, the target value s _{d is raised} to s _d '. The pressure maintenance area is thus moved upwards. This ensures that the pressure build-up phase begins at an early stage because, due to the change in acceleration, larger build-up movements are to be expected, which are still intercepted by the vibration dampers at this time.

With a still large jerk and now also a large acceleration a, the shift of the setpoint s _d to s' _{d is} maintained in situation C, because it can be expected that additional inertial forces have to be absorbed, and at the same time the permissible control deviation is reduced or halved in the illustrated embodiment. This measure increases the control speed so that the target value s' _{d is} quickly reached again. Now the jerk in situation D drops below the given threshold because z. B. approximately stationary cornering has occurred, the target level s' _{d is} shifted back to the initial value s _d and thus the pressure holding area _is again symmetrically arranged around the target level s _d . Otherwise, the roll motion could be overcompensated. In order to ensure a high control quality, the reduced permissible control deviation is initially maintained in situation D.

The control principle explained with reference to FIGS . 1 and 2 applies practically to each individual channel of a complete control system according to the invention, which is generally designed as a four-channel level control system. The interaction of the individual components of this four-channel control system is shown in FIG. 3. The most important components of the system are sensors and sensor circuits 20 to 24 of different types, evaluation circuits 25 , 26 and 27 , which process the sensor signals and via a valve control unit 28 Actuate valves 29 which determine the level in the four channels by keeping the pressure constant, pressure build-up or pressure reduction. The valve block 29 is also assigned one or more pumps 30 which generate the pressure or auxiliary pressure required to set the desired installation height in the four channels.

The signal evaluation and processing can be divided into three blocks 25 , 26 , 7 . In block 25 , the movements of the vehicle body are determined by evaluating the information supplied by the sensors and sensor circuits 20 , 21 . The vehicle longitudinal and lateral accelerations a _l and a _{q are} determined. Even if no assembly movements occur, when the acceleration or jerk threshold values are exceeded, the pump 30 is already activated by the output signal of the circuit 25 in order to compensate for dead times.

The actual four-channel control of the installation height is accommodated in block 26 . 22 designates the displacement sensors; a displacement sensor is arranged on each wheel or vibration damper, the output signal of which contains the information about the relative paths between the wheel and the vehicle body. Using filter algorithms, rad-specific regulation of the body height is carried out.

The third block 27 is used to monitor the control system. With the circuits that this block 27 contains, the displacement sensor signals ( 22 ), the output signals of the sensors 23 , which average the pressure in the individual shock absorbers, as well as the pressure determined by the sensor 24 , are evaluated. By logically linking the signals and applying plausibility considerations, it can be known from the information supplied to the monitoring circuit 27 whether the level control system is intact or whether an error must be present. A corresponding signal is triggered when an error is detected. In addition, in the event of a fault, the valves in the valve block 29 are switched to a safety state via the valve control unit 28 .

It is also a composite of the control system according to the invention with ABS / ASR systems and / or with a damping force control possible. In this case, especially the sensors exploit for the different systems. If you do not Sensors for determining the longitudinal and lateral acceleration of the You can now build from the steering angle, the brake pressure, the Brake pedal travel, the throttle valve angle, etc. the accelerations derive parameters. As a result, the manufacturing effort decreased.

FIGS. 4 and 5 finally show two possibilities for the design of the hydraulic system with which the level of height control by means of being in the control circuits evaluated information and he testified actuating signals can be performed in these circuits. In the exporting approximately example of FIG. 4, a central pressure supply system 31 is provided, which comprises a central hydraulic pump 32, a surge tank 33, and a central pressure accumulator 34. The pressure supply system 31 also includes three hydraulic valves 35 , 36 , 37 , a pressure relief valve 38 and a pressure sensor 39 . In addition, a pressure monitoring switch 40 is connected to the pressure accumulator 34 . The pressure supply system 31 is connected via a ge in the rest position locked, switchable to passage hydraulic valve 41 to 44 with the individual wheels or with the individual vibration dampers 45 to 48 and the associated pressure vessels 49 to 52 . There are five different states for the valve positions. In the idle state - pressure-free circulation - the valves assume the switching positions shown in Fig. 4. If the control is activated, the wheel with the largest setpoint overshoot and the one with the largest setpoint undershoot are determined first. Depending on the pressures in the two considered vibration dampers, the accumulator pressure and the absolute control deviations, the states: pressure compensation, pressure reduction, pressure build-up without accumulator or pressure build-up with accumulator are activated. The valve arrangement shown allows that during the pressure reduction phase the memory can be loaded simultaneously.

In the embodiment according to FIG. 5, which does not require a central pressure accumulator, multi-way valves 54 to 57 , each with three switching positions, are used in the paths from the central pressure supply system 53 to the individual vibration dampers 45-48 . In addition, there is a 2/2-way valve 58 in the connection path of the central pressure reservoir 33 '. About a further 2/2-way valve 59 in a pressure medium line 60 , the suction side of the pump 32 'is connected in the basic position to the container 33 '.

Pressure sensors 61 , 62 belong to the monitoring system.

The variant shown in Fig. 5 is characterized in that for the roll or pitch compensation (Druckmit telweg to the surge tank 33 'interrupted by switching the valve 58 ), two channels are always controlled ge, namely the one with the largest setpoint exceeded and the one with the largest drop below the setpoint.

Other valve configurations are also conceivable.

Claims (16)

1. Level control system for motor vehicles, consisting essentially of vibration dampers, which are arranged between the individual wheels and the vehicle body, from electrically operated valves with which a pressure medium flow between a pressure source, a pressure-free memory, the vibration dampers and the individual vibration dampers assigned Pressure vessels can be controlled, from displacement sensors for determining the body height and body movements, from sensors for direct or direct determination of the vehicle speed and the steering angle, and from an electrical circuit arrangement which evaluates the sensor signals and which contains a control circuit which is a function of a setpoint and the actual value of the body height of the vehicle, taking into account a permissible deviation between the setpoint and actual value, the valve actuation signals are generated, characterized in that this changes the longitudinal and lateral acceleration g, the so-called jerk () of the vehicle body evaluating circuit ( 2 ), the output signal of the control circuit ( 1 ) can be fed and shifts the setpoint of the body height (s _d ) when the jerk () a threshold (± _o ) exceeds, the direction of displacement depends on the direction of change, and that there is a circuit ( 3 ) evaluating the longitudinal and lateral acceleration (a) of the vehicle body, the output signal of which can be fed to the control circuit ( 1 ) and the permissible deviation of the actual value (see _a ) Varies from the setpoint (s _d ) of the body height or the permissible control difference (± d _o ). 2. Level control system according to claim 1, characterized in that the jerk () evaluating circuit ( 2 ) raises or lowers the setpoint of the height (s _d ) by a predetermined amount as soon as the jerk (a) a predetermined positive or . exceeds the negative threshold value (± a _o ). 3. Level control system according to claim 2, characterized in that for the displacement of the setpoint (s _d ) of the height, several threshold values are specified as a function of corresponding threshold values of the jerk occurring (). 4. level control system according to one or more of claims 1 to 3, characterized in that in a caused by the circuit ( 2 ) which evaluates the jerk () tet shifting of the setpoint (s _d ) of the body height, the permissible control deviation from the setpoint or control difference (± d _o ) is retained. 5. level control system according to one or more of claims 1 to 4, characterized in that the permissible control deviation or control difference (± d _o ) is reduced by a predetermined value when the longitudinal and lateral acceleration (a) a predetermined threshold value (± a _o ) exceeds. 6. level control system according to one or more of claims 1 to 4, characterized in that the permissible control deviation or control difference (± d _o ) continuously or in several stages depending on corresponding values of the longitudinal and lateral acceleration (a) and / or is increased. 7. level control system according to one or more of claims 1 to 6, characterized in that the longitudinal acceleration (a _l ) and the change (a _l ) of the longitudinal acceleration of the vehicle body are calculated or derived from the measured values obtained with the aid of wheel or axle speed sensors. 8. level control system according to one or more of claims 1 to 7, characterized in that the change (a _l ) of the longitudinal acceleration of the vehicle body from the brake pressure curve, the brake pedal travel, from the throttle valve angle of the vehicle drive motor or from the pitch angle or from a combination of these measured values is approximately derived. 9. level control system according to one or more of claims 1 to 8, characterized in that the lateral acceleration (a ₁ ) and the change in transverse acceleration (a) of the vehicle body from the longitudinal angle and the vehicle speed or from the roll angle or from a combination of these Measured values is derived. 10. level control system according to one or more of claims 1 to 9, characterized in that the jerk () evaluating circuit ( 2 ) activates the pressure source, for. B. by switching on a pressure medium pump ( 30 ) as soon as the jerk () exceeds a predetermined threshold value (± a _o ). 11. Level control system according to one or more of claims 1 to 10, characterized in that it is designed as a four-channel control system, a path sensor ( 22 ) being arranged on each wheel and the body height (s _{a1, 2, 3, 4} ) can be individually adjusted on each bike. 12. Level control system according to claim 11, characterized in that this is a central Druckversor supply system ( 31 ) with an electromotive hydraulic pump ( 32 ), with a pressure accumulator ( 34 ), with a surge tank ( 33 ) and in the connections to the hydraulic pump , to the pressure accumulator and to the pressure compensating hydraulic valve ( 35-37 ) and that the pressure supply system ( 31 ) has a locked in the rest position, switchable to passage hydraulic valve ( 41-44 ) to the individual vibration damper ( 45-48 ) with the associated Pressure vessels ( 49-52 ) is connected. 13. Level control system according to claim 11, characterized in that this is a central Druckversor supply system ( 53 ) with a hydraulic pump ( 32 '), with a pressure expansion tank ( 33 ') and with a hy draulic valve ( 58 ) in the connecting line of the pressure compensation tank ( 33 ') and that the Druckversor supply system ( 53 ) via a locked in the rest position hydraulic valve ( 54-57 ) to the individual vibration damper ( 45-48 ) is connected, in a second switching position of the hydraulic valves ( 54-57 ) the vibration damper ( 45-48 ) with the surge tank ( 33 ') and in a third switching position the hydraulic pump ( 32 ') with the vibration damper ( 45-48 ) are connected. 14. Level control system according to claim 13, characterized in that in one of the pressure side of the hydraulic pump ( 32 ') to the surge tank ( 33 ') leading line ( 60 ) and immediately before the connection of the surge tank ( 33 ') each in the rest position on passage switching valve ( 59 , 58 ) are inserted. 15. Level control system according to claim 14, characterized in that on the pressure side of the hydraulic pump ( 32 ') and before the isolating valve ( 58 ), which leads to the pressure compensation tank ( 33 '), each a pressure sensor ( 61 , 62 ) is connected . 16. Level control system according to one or more of claims 1 to 15, characterized in that it is equipped with a monitoring circuit ( 27 ), which with the help of the displacement sensors ( 22 ') determined on construction heights and movements, the pressure curve or pressure changes in the level control system, e.g. B. in the individual pressure vessels or in a central pressure accumulator ( 34 ), evaluates and, if there are error-indicating measured values or comparison values, triggers an error signal that switches the system into a safety state by activating the hydraulic valves or blocking the actuation.